How to joint two lines in AutoCAD 2017?

When trying to stretch a line to continue a path, or when doing joints and corners, I have a pain joining 2 lines together, either one of them is on top of the other or there’s a gap between the 2 lines, it’s like trying to solve a rubiks cube, when trying to find that one line that is not joined properly, any tips?

Autocad is pretty good software, it hardly seems fair to blame the software for what will almost certainly turn out to be UIE (user induced error).
ReMark is right, no shortage of folks willing to help here on the forum.
Try using the FLATTEN command before trying to join them, perhaps that will help.
If you were having difficulty with JOIN in the PEDIT command, make sure that when you see the FUZZ DISTANCE prompt you hit ENTER, so that the command will complete.
If you ignore that and ESCAPE, they will not be joined.